Molecular Complex as a Charge-Transfer Agent at the Lithium Interface for Dendrite-Free Cycling

Abstract

The practical realization of lithium metal batteries (LMBs)─long hailed for their high theoretical energy density─continues to be impeded by the persistent challenge of lithium dendrite formation, which compromises safety and cycling stability. In this study, we introduce 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (TPP) as an electrolyte additive to suppress dendritic lithium growth. The porphyrin additive forms an in situ lithium-TPP complex at the Li metal interface, which facilitates the interfacial charge transfer and homogenizes the Li⁺ flux, thereby stabilizing the lithium metal deposition. Symmetric cells incorporating 20 mM TPP in a commercial electrolyte, with a thin polymeric separator that offers minimal resistance to dendritic penetration, exhibit stable cycling for over 1000 h at 0.5 mA cm^–2 without short-circuiting and stable voltage response under increasing current, significantly outperforming the reference cell without the TPP-containing electrolyte, which suffers rapid short-circuit failure. Scanning electron microscopy reveals a compact lithium morphology with the TPP-modified electrolyte, while operando solid-state ⁷Li NMR spectroscopy during symmetric Li-cell cycling confirms the suppression of dendrite formation. Full cells using Li₄Ti₅O₁₂ cathodes demonstrate 90% capacity retention over 150 cycles, with a Coulombic efficiency of 99.9%. These results highlight the potential of porphyrin-based additives in enabling safe and long-lasting lithium metal batteries, and may inspire broader exploration of molecular complexes as a dynamic interphase in next-generation energy storage systems.